The present invention relates to an image forming apparatus such as an electrophotographic copying apparatus, electrostatic recording apparatus or the like, and more particularly to grounding of a photoreceptor drum in the image forming apparatus.
In an image forming apparatus such as an electrophotographic copying apparatus, an electrostatic recording apparatus or the like, a desired image is obtained by the following operations: an image carrier is used which is a rotation type photoreceptor drum having a photoconductive light sensitive layer on its circumferential surface; after the light sensitive layer has been charged, a document image is exposed while the photoreceptor drum is being rotated; thereby, an electrostatic latent image of the document is formed on the light sensitive layer; toners are adhered onto the electrostatic latent image by developing units so as to form a visual image; and the obtained toner images are transferred onto a recording sheet, and the sheet is fixed so as to obtain the desired image.
The image carrier, which is a photoreceptor drum, is structured as an integral unit which can be detachably provided in the image forming apparatus main body together with a charger, developing units, and a cleaning unit, and forms a process cartridge. The process cartridge can be attached to and detached from the apparatus main body, when necessary, for inspection, cleaning, and repair of the apparatus, or in the case of replacement of the cartridge, when its life has expired. The image forming apparatus structured as described above is widely marketed because of its superior maintainability.
The photoreceptor drum which is incorporated in the process cartridge is pivotally provided in a casing of the cartridge, and is rotated by the driving force from a rotational driving section at a constant speed in the predetermined direction. Further, the rear surface of the photoreceptor drum is directly grounded, or grounded through an appropriate power source so as to obtain an excellent image. Therefore, the process cartridge is structured in the manner that: it is guided through a guide member provided between the process cartridge and the apparatus main body, to be attached to and detached from the apparatus; a positioning pin provided to the process cartridge is inserted into a receiving hole of the apparatus main body, at an end position of the process cartridge insertion; positioning of the process cartridge with respect to the apparatus main body is carried out; and at the same time, grounding is carried out through the positioning pin and the receiving hole.
When the process cartridge is loaded in the apparatus main body, it is necessary to ground the photoreceptor drum, which is incorporated into the process cartridge, to the apparatus main body. In this case, as described above, the method for grounding is carried out as follows: the positioning pin provided on the process cartridge is connected with the receiving hole, which is provided to the apparatus main body, when the process cartridge is loaded in the apparatus main body.
As described above, in the case of connection of the positioning pin with the receiving hole, the connection relies on point contact or line contact, and therefore, positive electrical connection such as surface connection due to surface contact is not always perfectly accomplished. Especially, when the accuracy of parts, the accuracy of assembly, or the like is not so good, the electrical connection becomes more unstable. Under the above described condition, the electrostatic latent image formed on the photoreceptor drum can not be stable and of high quality, so that the developed image can not be of high quality, either.